In the semiconductor integrated circuit (IC) industry, technological advances in IC materials and design have produced generations of ICs where each generation has smaller and more complex circuits than the previous generation. In the course of IC evolution, functional density (i.e., the number of interconnected devices per chip area) has generally increased while geometry size (i.e., the smallest component (or line) that can be created using a fabrication process) has decreased. This scaling-down process generally provides benefits by increasing production efficiency and lowering associated costs. Such scaling down has also increased the complexity of IC processing and manufacturing.
A photolithography process forms a patterned resist layer for various patterning processes, such as etching or ion implantation. The minimum feature size that may be patterned by way of such a lithography process is limited by the wavelength of the projected radiation source. Lithography machines have gone from using ultraviolet light with a wavelength of 365 nanometers to using deep ultraviolet (DUV) light including a krypton fluoride laser (KrF laser) of 248 nanometers and an argon fluoride laser (ArF laser) of 193 nanometers, and to using extreme ultraviolet (EUV) light of a wavelength of 13.5 nanometers, improving the resolution at every step.
In the photolithography process, a photo mask (or mask) is used. The mask includes a patterned image that may be used to transfer circuit and/or device patterns onto a semiconductor wafer by the photolithography system. Defects are not allowed to be formed on the photo mask, in order to achieve a high-fidelity pattern transfer from the patterned photo mask to the semiconductor substrate. Particles deposited on the surface of the photo mask may cause the lithographically transferred patterns to degrade. Particles may be introduced by any of a variety of methods such as during a chemical mechanical polishing (CMP) process, a cleaning process, and/or during the handling of the photo mask.
Consequently, it is desirable to provide a solution for protecting the photo mask from falling particles.